The streets of Charleston, South Carolina, vanished beneath water on Thursday as Hurricane Dorian skirted the US coast after reducing parts of the Bahamas to rubble.
At least four storm-related deaths have already been reported in the US, according to Reuters.
In the Bahamas, the death toll rose to at least 23 people on Thursday.
In the Carolinas alone, more than 900,000 people had been ordered to evacuate their homes.
More than 210,000 homes and businesses were without power in South Carolina and Georgia early on Thursday, according to local electric companies.
Life-threatening storm surges and dangerous winds were possible in much of the coast of South Carolina, North Carolina, Maryland and Virginia, the National Weather Service said.
Dorian whipped up at least three tornados in the region, officials said.
Governors in the region declared states of emergency, closed schools, opened shelters, readied national guard troops and implored residents to take warnings seriously.
70,000 Bahamians in need of emergency relief
At least 70,000 Bahamians needed immediate humanitarian relief after Dorian became the most damaging storm ever to hit the island nation.
Mark Lowcock, United Nations under-secretary-general for humanitarian affairs, said in a conference call from the Bahamas that people needed food, shelter and medical assistance.
"There is concern that some whole communities' locations have been destroyed or are underwater or washed away," he said.
"One of the uncertainties is where the people who were living there are now and how to reach them."
Aerial video of the worst-hit Abaco Islands in the northern Bahamas showed widespread devastation, with the harbour, shops and workplaces, a hospital, and airport landing strips damaged or blown to pieces, all of which is frustrating rescue efforts.